Two loud explosions shook the airport in Zaventem, a Brussels suburb, early Tuesday, and a blast also rocked Maalbeek station on the Brussels Metro, close to European Union buildings. Preliminary reports said 21 people have died.

“U.S. markets look set for a lower open as risk-off sentiments look to cross the pond in the wake of more terrorist attacks in Europe,” said Jasper Lawler, a CMC Markets analyst, in a note.

“Safe haven assets are rising quickly this morning in response to the two explosions in Brussels Airport,” said Nour Al-Hammoury, chief market strategist at ADS Securities, in a note. “Gold, silver and the yen are all up.”

Gold futures GCJ6, +0.68% gained 0.7% on apparent haven demand after the attacks, while silver futures SIK6, +0.49% rose 0.8% and the dollar USDJPY, -0.29% was down about 0.4% against Japan’s currency.

Casulty in the blast

On Monday, the S&P 500 SPX, +0.10% closed 0.1% higher, while the Dow DJIA, +0.12% gained 0.1%, or 21.57 points, rising for the seventh session in a row.

Individual movers: Airlines JETS, +0.63% and other travel-related stocks look set to come under pressure after the Brussels attacks, as shares in European carriers moved sharply lower.

Apple Inc. shares AAPL, -0.27% dipped in premarket trading after some analysts said the iPhone maker’s product event on Monday was underwhelming. Meanwhile, a court hearing to determine whether the government can force the tech giant to weaken its iPhone security has been postponed, as the FBI may be able to break in without Apple’s help.